Challenges and Opportunities In Crashworthiness Certification of Composite-Intensive Airframe Structures

AMTAS – University of Washington

UW PI: Paolo Feraboli

UW Students: Bonnie Wade, Morgan Osborne (Boeing), Max Spetzler

Boeing PI: Mostafa Rassaian, BR&T

FAA PI: Larry Ilcewicz and Allan Abramowitz

JAMS PM: Curt Davies

Presented by Rassaian at the Baltimore, MD JAMS Meeting in April 2012

JAMS RESEARCH BACKGROUND

Background

• CMH-17 (former MIL-HDBK-17) Working Group supports the development of a self-contained section of the handbook on composite Crashworthiness and Energy Management.

• Aim is to generate and present for the first time in a concise and comprehensive fashion, recommended practices and guidelines for the experimental and numerical characterization of the crash behavior of composite-intensive airframes.

• Focus of the WG are regulatory agency requirements and industry methods of compliance for crashworthiness certification.

• The Crash WG activities have increased every year, drawing larger membership and attendance each meeting.

Background

• WG formed in March 2005 at the Charlotte meeting by PF • Automotive and Aviation (Industry & Government) founding

members

• From its inception, the key areas that were identified for investigation:

– Test standard and experimental guidelines – Certification and compliance methodology guidelines

Context: in March 2005 the Boeing 787 was just launched and the Special condition had not been issued

Revision G Accomplishments

• In 2005-2006 wrote an introductory section on Composite Crashworthiness, which was approved for publication in the Yellow Pages.

• This section now constitutes Chapter 14 in Vol. 3B of Rev. G

Analysis focus

• Mostafa Rassaian of Boeing joins at Chicago meeting in July 2006

• Emphasis placed on numerical/ analytical needs • Becomes co-chair and spearheads the creation of a Round

Robin (RR) exercise to assess predictive capability of commercial FEA codes

• Various users with multiple codes and different modeling strategies join the effort

• RR begins January 2008 at Cocoa Beach meeting

FEA Round Robin

• The RR focuses on evaluating the capability of commercial FEA analysis tools and modeling strategies to simulate the crush energy absorption of composite structural elements.

• In 2011-2012 the Numerical Round Robin effort will be completed, and a new section will be incorporated into the Handbook.

• LS-DYNA MAT58 M. Rassaian (Boeing BR&T) • LS-DYNA MAT58 X. Xiao, V. Aihataraju (G.M.) • LS-DYNA MAT54 P. Feraboli (U. of Wash.) • LS-DYNA MAT162 R. Foedinger (MSC Corp.) • PAMCRASH CDM A. Johnson (DLR) • RADIOSS Plasticity JB Mouillet (Altair) • RADIOSS Tsai-Wu A. Caliskan (Ford) • ABAQUS C-Zone G. Barnes (Engenuity)

Abaqus VUMAT (Indermuhle) and PAMCRASH crushfront (Pickett) abandoned early on

Roadmap for CMH-17 RR Crashworthiness Pr

oble

m S

ize/

Sca

le

axial crush

axial crush

dynamic crush of c-channel sub-assembly quasi-static and

dynamic test

sub-assembly level test & simulation

joint characterization and strain rate

sensitivity

sinewave

c-channel

Deleted

RR observations

• All approaches and codes can reproduce successfully the experimental results (with different accuracy)

RR observations

• However, none of them are truly “predictive” but need to be used in the context of a Building Block Approach

• Example below shows how the PAMCRASH model by Alastair Johnson at DLR needs to be tweaked significantly to predict the right crush behavior for 3 different shapes

Courtesy: Alastair Johnson (DLR)

Working Group Membership

• The Working Group has recently been divided in three Task Groups, each focusing on a specific aspect of crashworthiness.

• Very active contributors have also been Karen Jackson (NASA Langley), Kevin Davis (Boeing BCA) and Michael Mahe (Airbus).

JAMS RESEARCH CONTRIBUTIONS

JAMS Research Accomplishments to date

• Experimental characterization (Feraboli, Wade) – 100% complete – Several publications

• LS-DYNA MAT54 characterization (Wade, Deleo) – 70% complete – 1 FAA Tech Report delivered and in press

• LS-DYNA MAT54 CMH-17 RR entry (Wade) – 100% Results and write-up

Experimental focus: UW activity

• UW initial activity focused on test methods • Flat coupon derived from NASA proposed method

– “Development of a modified flat plate test and fixture specimen for composite materials crush energy absorption” – Feraboli P. – Journal of Composite Materials, published online July 2008.

• Self-stabilizing coupon (corrugated/ sinusoidal) – “Development of a corrugated test specimen for composite materials energy

absorption” – Feraboli P. – Journal of Composite Materials - 42/3, 2008, pp. 229-256

• Effect of curvature (from flat to self-stabilizing) – “Crush energy absorption of composite channel section specimens” – Feraboli, P.,

Wade, B., Deleo, F., Rassaian, M. – Composites (Part A), 40/8, 2009, pp. 1248-1256.

Experimental focus

• Energy absorption (SEA) is NOT a material property

LS-DYNA MAT54

• Began using LS-DYNA MAT54 after advice and based on guidance of Dr. Mostafa Rassaian

• No LS-DYNA Capability prior to that at UW ACSL • Assessed robustness of MAT54 to modeling sinusoidal

specimen – P. Feraboli, B. Wade2, F. Deleo2, M. Rassaian1, M. Higgins1, A.

Byar1, “LS-DYNA MAT54 modeling of the axial crushing of a composite tape sinusoidal specimen”, Composites (Part A), doi:10.1016/j.compositesa.2011.08.004

– Detailed FAA Tech Report submitted and in press

Some key results

• Accurate matching of experimental results can be achieved • MAT54 not purely predictive: MAT CARD needs to be tweaked

to predict crushing of different shapes

• SOFT Crashfront parameter very influential

JAMS Research Ongoing activities

• Educational Module (Feraboli) – 80% complete – Lecture recorded and presentation ready

• LS-DYNA MAT54 characterization (Wade, Osborne) – Completing element level work – Completing single-element studies

• CMH-17 RR write-up (Wade) – Mostafa and Paolo with Bonnie to complete summary of RR effort

• Cert protocol/ guidelines document (Spetzler) – 15% complete

Educational Module

• 2 hr module within the 80 hr course • Introduction to crashworthiness

Single element study

• In-depth single element simulations study MAT54 input parameters using simple layups:

– UD [0]12 – UD [90]12 – cross-ply UD [0/90]3s – fabric [(0/90)]8

• Goal is to determine critical parameters for ply failure and element deletion

ust at o

XY

dy dyN1

N2 N3

N4

Global CS

12

Matl.CS

Single element study: UD

• Elastic properties are not zeroed after strength-based failure • Failure strains determine element deletion, and can either

prematurely delete an element or add a significant amount of energy to the element output ε

0

Case 2:DFAILM =

YT/EB

= Element Deletion

ε

σ

DFA

ILM

YT

/

Y /

DFA

ILM

= MT “fail” (em)

ε

/

ε

σ

Case 4:DFAILM >

YT/EB

YT

YTEB

ε

σYT

YTEB

Case 2: <

YT/EB

DFA

ILM

σ

Case 4:

YT

= Element Deletion =

ε

/

Strength-based failure

Failure strain too low Correct failure strain Failure strain too high

Single element study

• Although failure strains are the most significant MAT54 parameter, there is only one failure strain input for the matrix direction such that a large plastic region must exist in the 2-dir tensile stress-strain curve

-300

-200

-100

0

100

200

300

400

-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Stre

ss [k

si]

Strain [in/in]

Axial

Transverse

-40

-30

-20

-10

0

10

20

30

40

-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Stre

ss [k

si]

Strain [in/in]

Single element study: fabric

• UD and fabric lamina properties are input for the [0/90]3s and [(0/90)]8 laminates, respectively

• In MAT54, the [(0/90)]8 fabric is modeled as a [0]8 laminate with fabric properties

• MAT54 uses the UD lamina properties and CLT to determine the behavior of the [0/90]3s laminate

F1tu F1cu F2tu F2cu ε1tu ε1cu ε2cu UD 319000 213000 7090 28800 0.0174 -0.0116 0.024 FABRIC 132000 103000 112000 102000 0.0164 -0.013 0.014

ust at o

XY

dy dyN1

N2 N3

N4

Global CS

12

Matl.CS

Single element study: fabric

• The fabric element shows a linear-elastic brittle behavior • The UD cross-ply results show low-energy plastic regions

after the failure of the 0-degree plies, which terminate only after the 90-direction failure strain value (0.024 in/in) is achieved

F1tu F1cu ε1tu ε1cu Crossply 163000 120900 0.0174 -0.0116 FABRIC 132000 103000 0.0164 -0.013

Expected laminate output:

-150

-100

-50

0

50

100

150

200

-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Stre

ss [k

si]

Strain [in/in]

UD Crossply

Fabric

Cert protocol

• Crashworthiness Certification protocol: Building Block Approach adapted to Crashworthiness

• Based on Analysis supported by test evidence • Successfully adopted by Boeing for 787 to meet Special

Condition

• Cert by test not likely to be an option for Part 25 but may be considered for Part 23

Courtesy: Boeing

Example of cert protocol for B787

Coupon Element Subcomponent

Component Large scale Large scale

Courtesy: Boeing

Cert protocol

• Develop a guidance document that contains an example of a certification protocol for Part 25 aircraft based on a generic geometry

• Indicate a path toward certification of a virtual aircraft for crashworthiness:

– Certification strategy – List of Allowables tests – Definition of Element level tests – Definition of component and subassembly tests – Definition of analyses and analysis-correlation

procedures

– Validation and large-scale test expectations

Cert protocol

• Identify a suitable mock geometry, with all relevant structural features (floors, floor beams, floor supports, etc.)

• Synthetize the wording of a mock Special Condition into a series of requirements

• Define a series of methods of compliance with such requirements

• Lay-out the details of the certification protocol for such mock configuration

• Aid the FAA in the development of guidance material for crashworthiness certification for the transport industry, and in the preparation of educational/training material for new engineers.

General configuration Part 25 fuselage

Research to be continued

Completed by September 2012 • All LS-DYNA MAt54 work (single element and higher level

structures) • Initial draft of test protocol for Mock Certification • Transcribe lecture notes and complete educational module • Complete CMH-17 RR writeup

To be continued in 2013 • Complete test protocol for Mock certification • Complete analysis protocol for Mock certification • Provide support material for guidance documents

Challenges and Opportunities In Crashworthiness Certification of Composite-Intensive Airframe Structures�AMTAS – University of WashingtonSlide Number 2BackgroundBackgroundRevision G AccomplishmentsAnalysis focusFEA Round RobinRoadmap for CMH-17 RR CrashworthinessRR observationsRR observationsWorking Group MembershipSlide Number 12JAMS Research Accomplishments to dateExperimental focus: UW activityExperimental focusLS-DYNA MAT54Some key resultsJAMS Research Ongoing activitiesEducational ModuleSingle element studySingle element study: UDSingle element studySingle element study: fabricSingle element study: fabricCert protocolExample of cert protocol for B787Cert protocolCert protocolGeneral configuration Part 25 fuselageResearch to be continued